Please don’t get an Omlet. They are not recommended. The enclosed part is far too small and given piggies should not be on wet or cold grass, or out in winter, then you will very quickly run into trouble with an omlet through lack of safe enclosed space.
You will require a good strong, wooden hutch, with insulating and waterproof covers, plus additional insulation on the hutch and probably blankets as well
For winter you will also need heatpads and lots of hay (straw is not recommended).
For summer they will need to be somewhere heavily shaded and out of warm breezes. Unfortunately hutches and sheds can and do become death traps.
For two sows you need a 150x60cm hutch, for two boars you need a 180x60cm hutch.
If you have a shed, then that is ideal for the hutch to be put into in winter. Piggies are not hardy and if does take a lot of work to keep them warm enough outside.
My boys live in a hutch in my shed (free roam the shed). The shed offers great benefit in winter as it provides protection from the elements but I always have a spare cage and plan to bring them indoors if needed. Even with the protection of the shed, they still have a thermal cover, two blankets, a waterproof cover and a duvet on the hutch, along with four heatpads between the two of them.
But, summer is the worst part - in the outside/shed is so much harder and mine have had to move into the house every summer for the past four years due to the heat in the shed (40 degrees plus) and on the lawn. It just hasn’t been safe to have them outside